Disruption of blood-retinal barrier at the retinal pigment epithelium after systemic urea injection

Electron microscopic studies were done on the structural alterations of retinal pigment epithelial cells occurring under osmotic stress utilizing rhesus monkeys and lanthanum nitrate as a tracer. Fluorescein fundus angiography revealed leaking points of fluorescein from the choroid to the retina, and various degenerative alterations of the retinal pigment epithelial cells were observed in these leaking areas. Some cells included many vacuoles in their cytoplasm, but diffusion of lanthanum from the choroid to the outer segment of visual cell was obstructed by the tight junctions between the retinal pigment epithelial cells. Other cells were severely damaged with ruptured membranes. Abundant tracer material diffused through the cytoplasm into the subretinal space. Other cells were broken down in an isolated manner and here marked extravasation of lanthanum into the subretinal space was observed.